As the conventional electric motor to which the present invention is directed, there can be mentioned an electric motor as shown in FIGS. 5A and 5B. More specifically, many cut grooves 2 are formed at constant intervals on the inner circumferential face of a stator 1 having an inner face of a cylindrical shape, which is formed of a laminated iron core of an electromagnetic steel sheet, a winding 3 being inserted in the grooves and a front bracket 5 and a rear bracket 14 being fixed to the stator 1 by bolts 12. Each bracket protects the end portions (coil ends) of the winding projecting frontward and backward from the stator and supports each of the bearings 10 and 11 of a shaft 8 of a rotor proper 6 formed of a permeable material and having a magnet plate 7 arranged on and fixed to the peripheral face thereof.
As shown in FIGS. 6A and 6B, the assembly of the rotor in this electric motor is performed by fitting and fixing the front bearing 10 and rear bearing 11 to the front and rear parts of the shaft 8 of the rotor proper 6 having a magnet arranged on and fixed to the peripheral face thereof, inserting the rotor into the stator while taking care that the magnet 7 on the peripheral face of the rotor does not impinge against the inner circumferential face of the stator 1, fitting the front bearing 10 into the recess R.sub.1 of the front bracket 5 as shown in FIG. 5A, engaging the recess R.sub.1 of the rear bracket 14 with the rear bearing 11, and securing both brackets 5 and 14 by bolts 12.
Most magnets used at present for industrial purposes are formed of materials which are easily chipped, and therefore, at the step of inserting a rotor in the manufacture of a conventional electric motor as shown in FIGS. 5A and 5B, if there is even a slight deviation .DELTA. between the axis X--X of the stator and the axis X.sub.1 --X.sub.1 of the rotor, as shown in FIG. 6A, since the difference between the outer diameter d.sub.3 of the rotor and the inner diameter D of the stator is small, at the point P.sub.1 shown in the drawings, the lower end E of the outer face of the rotor impinges against the upper end T.sub.1 of the inner face of the stator and the lower end E of the magnet is chipped.
Furthermore, as shown in FIG. 6B, if the rotor is inserted in the state where the axis X.sub.1 --X.sub.1 of the rotor is slightly inclined to the axis X--X, the lower end E of the outer face of the magnet impinges against the inner face of the stator, which is a coarse face of the laminate of the electromagnetic steel sheet, at the point P.sub.2 in the drawings, and at the point P.sub.2.dbd. the upper end T.sub.1 of the inner face of the stator impinges against the surface of the magnet, with the result that the magnet is damaged at the two points P.sub.2 and P.sub.2.dbd.. Where the magnet has already been magnetized, the rotor is assembled in the state where most of the chipped magnet pieces are attracted to the surface of the rotor or the inner face of the stator by the magnetic force.
Where the rotor is built in an electric motor together with these magnet pieces, problems such as non-rotation of the rotor and hitching during the rotation are caused.
Where the magnet on the peripheral face of the rotor already has an attracting force as the permanent magnet at the assembling step, the magnet is apt to adhere to the inner face of the stator during the insertion, and since the inner face of the stator is coarse, there is a risk of damaging the magnet only by attraction by the magnetic force.
The present invention provides a method for improving the assembling method which involves the above-mentioned difficulties and in which the efficiency is low and defective products are often formed, and further, provides an electric motor having a structure to which the improved assembling method is easily applied.